1. Field of the Inventions
The present inventions relate to a control system for a boats, such as planing boats with water-jet-propulsion systems.
2. Description of the Related Art
Small planing boats, such as “personal watercraft” are often used for sports and leisure. Boats of this type of are usually small planing boats, driven by a rearward discharge of a jet of water drawn from a water intake port provided to an under surface of the boat body, then pressurized and accelerated by a water-jet pump.
Meanwhile, maximum speed limits for small planing boats is, in some local regions, limited. Thus, manufacturers may be required to install a vessel speed (cruising speed or boat speed) limiter in order to prevent the boat from exceeding a predetermined maximum speed limit.
Some boats include user-adjustable vessel speed control systems, also known as “cruise assist systems,” such as those disclosed in Japanese Patent Document JP2002-180861A1. In this patent, the vessel speed control system includes a cruise assist operation device provided on a steering bar, and according to the operation of this device, the engine of the boat is maintained at an engine speed stored in a memory device.
However, in such speed control systems in which vessel speed is controlled based only on the engine speed stored in memory, the actual vessel speed varies with the shape and weight of the boat body and conditions of the engine. Other conditions such as a direction of the wind, current, loading weight (for example, a body weight and the number of people boarding the boat), etc. also affect the vessel speed.
Thus, this type of speed control system suffers from problems in that the vessel speed is not satisfactorily controlled when conditions are changed. In addition, the maximum speed limit for marine vessels is different for different countries and/or different regions.
Therefore, in order to cope with these situations, one solution is to change conditions of the boat body without changing the set conditions of the speed control system. For example, the shape of the boat body can be changed to have a larger resistance to water in order not to exceed the regulatory speed. However, if such maximum speed control technique is adopted, larger resistances are also generated during acceleration, so that output power of the engine is not always effectively utilized, and thus can be unsatisfactory to users.